When entering the 21st century, the worldwide infrastructure construction is ushered in the climax of “underground space” development, and the scale and quantity of tunnel construction serving as a main structural form of underground engineering are increasing. Tunnels are mainly divided into highway and railway traffic tunnels, water conservancy transfer tunnels, municipal pipeline tunnels, mine tunnels and the like. For the tunnel engineering constructed under complex geological conditions, the geological status of a line region is difficult to verify at the early geological exploration stage, so that geological disasters such as water and mud outburst, collapse and large deformation frequently happen in construction, and the construction safety is seriously affected. For example, Japan's Seikan undersea tunnel was submerged twice in 1969 and 1976 due to water outburst accidents, wherein 33 persons died, more than 1,300 persons were disabled, and the construction period was delayed by more than 2 years; and in the construction process of China's Yuanliangshan Tunnel, totally 71 times of large-scale mud and stone outburst and water and sand burst happened, the construction safety was seriously threatened, and the construction period was delayed. Therefore, advanced detection is quite necessary for the geological condition in front of a tunnel face, to detect the geological structure which may induce geological disasters, such as a karst cave, an underground river, a fault or the like.
Advanced geological prediction of a tunnel is to detect the geological condition in front of an excavated face of the tunnel by means of drilling, geophysical exploration and the like, and master the structure and property of a tunnel surrounding rock in front as well as the condition of the unfavorable geological structure such as a karst cave, an underground river, a fault or the like before construction, so as to provide guidance for further construction, avoid the geological disasters such as water and mud outburst, collapse and large deformation and ensure the construction safety. In the study and practice of the advanced geological prediction of a tunnel construction period, it is discovered that the detection effect of a single method is not ideal and the problems of inaccurate qualitative judgment, low positioning precision and the like always appear due to the multiplicity of geophysical inversion interpretation and the complexity of environment detection, so that false reporting, underreporting or misreporting is produced, and serious hidden danger is caused for the construction safety. To improve the reliability and accuracy of the advanced geological prediction, multiple prediction methods are combined with each other to implement integrated advanced geological prediction, and various prediction results are verified by each other and complemented with each other, so that the detection effect may be effectively improved.
To disclose the geophysical response characteristics of a typical unfavorable geology, establish a three-dimensional positioning and water quantity estimation and quantitative identification method for the unfavorable geology in front of a tunnel, research and develop a novel geophysical detection technology, verify the detection effect and evaluate the performance of the devices, it is very important to establish a tunnel construction large-scale integrated geophysical advanced detection model test device. The geophysical detection model test, which may be used for constructing a known geological condition and simulating a real detection environment and a detection object, plays a very important role in verifying the detected performance effect.
The physical model test of geophysical detection indicates that a similar model is built from a physical prototype of a medium in a test room based on the physical and geometrical similarity criteria according to a certain scale factor, to simulate the real detection environment in the actual geological condition. A relationship between the model structure, structure, physical properties and change rule of the medium and the characteristics and change of a geophysical field is established by observing the geophysical field in the model. The physical prototype may be studied and detected by using the relationship according to the geophysical field observed on the physical prototype of the medium. The geophysical detection test is an important path and means for basic theory and method technical studies of solid geophysics and exploration geophysics.
In view of development of the present model test, the existing model test has the limitation of single detection means, small scale, single simulated geological type, material non-repeatability and the like, e.g. the model test device in the document Goaf Two-Dimensional Ultrasonic Physical Model Experimental Studies (Zhao Jiafu, Journal of Jilin University) only aims at a seismic wave method, and the model consisting of an organic glass plate of 80 cm×20 cm×0.3 cm and a water trough is small in scale; and the model test in the document Physical Simulation of Total Space Transient Electromagnetic Response in Tunnel (Qi Taiyue, Modern Tunnelling Technology) only aims at a transient electromagnetic method, the model size is 4 m×2 m×1.5 m, the internal material is fixed and the simulated geological type is single.
With respect to the investigation of the existing technology, the tunnel construction integrated advanced geological prediction physical simulation technology and devices face the following main problems: (1) for realizing similarity physical simulation of three detection methods including a seismic wave method, an electromagnetic method and a direct-current electric method, the similarity principles of the detection methods are different from each other, and the requirements for parameters of test materials are also different from each other, so it is difficult to find a similar material capable of simultaneously satisfying the three detection methods; (2) for really simulating the actual geological condition and detection environment and meeting the boundary requirements of propagation of a seismic wave field, an electromagnetic field and a direct-current electric field, large size and scale of the physical model test device is required; (3) multiple water-containing geological structure devices for karst caves, underground rivers, faults and the like are used in actual construction, and in order to classify and study the geophysical response and detection identification effects of the typical water-containing geological structure devices, different types of water-containing geological structure devices need to be simulated in the physical model test; (4) because the cost of the physical model test is relatively high, and if only the single geological condition is simulated, geological abnormal bodies and similar materials are not replaceable or reusable, the study cost is greatly increased, and quick arrangement of different types of abnormal bodies is required to simulate different geological conditions; (5) each existing physical model test device is only designed for a certain detection means, however, the geophysical detection has the characteristics of multiplicity and detection environment complexity, the physical test device is required for multiple detection methods such as the seismic wave method, the electromagnetic method and the direct-current electric method, and the results of these detection means need to be compared and verified, whereas how the observation systems of various detection means are arranged in a physical model so as not to interfere with each other is a problem.